I[ll now answer my own question
The six different seat back pieces are each held on by a combination of hangers and screws. One would think that the hangers, which are attached through a cutout in the back of the cushion, would have been for the purpose of allowing easy removal of the cushion. However, the screws totally restrict that inasmuch as it seems obvious that the cushions and the screws were assembled before the inside wall of the boat was fastened to the hull during the manufacturing process. There is no way humanly possible to remove the screws without damaging something in the process. But, in my case I believe, I will be able to repair the slight damage to each screw hole in the fiberglass and, since my newly covered cusions will cover it all up, it will be fine. I have no intention of putting screws into anything I'm doing. I plan to use velcro instead if anything at all is needed in addition to the hangers which seem to be perfectly good.
I trust that this information might be of interest to Bayliner and Sea Ray owners as well.